Pulse modifier with adjustable etendue

ABSTRACT

A beam modifying unit increases both temporal pulse length and Etendue of an illumination beam. The pulse modifying unit receives an input pulse of radiation and emits one or more corresponding output pulses of radiation. A beam splitter divides the incoming pulse into a first and a second pulse portion, and directs the first pulse portion along a second optical path and the second portion along a first optical path as a portion of an output beam. The second optical path includes a divergence optical element. A first and a second mirror, each with a radius of curvature, are disposed facing each other with a predetermined separation, and receive the second pulse portion to redirect the second portion, such that the optical path of the second portion through the pulse modifier is longer than that of the first portion, and the separation is less than radius of curvature.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Non-Provisional application ofSer. No. 12/615,328, filed Nov. 10, 2009, (that issued as U.S. Pat. No.8,004,770 on Aug. 23, 2011), which claims benefit under 35 U.S.C.§119(e) to U.S. Provisional Patent Applications: 61/142,004, filed Dec.31, 2008 and 61/149,828, filed Feb. 4, 2009, which are all incorporatedby reference herein in their entireties.

FIELD

The present invention generally relates to lithography, and moreparticularly to illumination pulse modification.

BACKGROUND

Lithography is widely recognized as a key process in manufacturingintegrated circuits (ICs) as well as other devices and/or structures. Alithographic apparatus is a machine, used during lithography, whichapplies a desired pattern onto a substrate, such as onto a targetportion of the substrate. During manufacture of ICs with a lithographicapparatus, a patterning device, which is alternatively referred to as amask or a reticle, can be used to generate a circuit pattern to beformed on an individual layer in an IC. This pattern can be transferredonto the target portion (e.g., comprising part of, one, or several dies)on the substrate (e.g., a silicon wafer). Transfer of the pattern istypically via imaging onto a layer of radiation-sensitive material(e.g., resist) provided on the substrate. In general, a single substratecontains a network of adjacent target portions that are successivelypatterned.

Known lithographic apparatus include steppers, in which each targetportion is irradiated by exposing an entire pattern onto the targetportion at one time, and scanners, in which each target portion isirradiated by scanning the pattern through a radiation beam in a givendirection (the “scanning” direction) while synchronously scanning thesubstrate parallel or anti-parallel to this direction. It is alsopossible to transfer the pattern from the patterning device to thesubstrate by imprinting the pattern onto the substrate.

Typically, an excimer laser is used to supply the lithographic apparatuswith radiation in the form of pulsed beams of radiation, e.g., highintensity ultraviolet pulses. Large, expensive lens elements can degradeafter receiving billions of the pulses. Optical damage can increase withincreasing intensity (i.e., light power (energy/time) per cm² ormJ/ns/cm²) of the pulses. The typical pulse length from these lasers isabout 20 ns, so a 5 mJ laser pulse would have a pulse power intensity ofabout 0.25 mJ/ns (0.25 MW). Increasing the pulse energy to 10 mJ withoutchanging the pulse duration would result a doubling of the power of thepulses to about 0.5 mJ/ns, which can significantly shorten the usablelifetime of the lens elements.

Pulse stretchers can be configured for use with a lithographic apparatusto minimize optical damage and degradation by substantially increasingthe pulse length. Increased pulse length is accomplished by creatingcopies of the pulse, where each copy is separated in time by using anoptical delay.

Using known pulse stretching units can require an initial re-calibrationof the lithographic apparatus. Also, the pulse stretching units can haveno ability to control the size or direction of the beam withoutadditional periodic calibration.

In addition, pulse stretching units can suffer from the generation ofdynamic speckle. Speckle is a function of both the pulse duration aswell as the Etendue of the beam. Speckle can be caused by a finite pulselength and limited spectral linewidth of partially coherent radiationfrom the laser. Speckle can cause a micro non-uniformity of the dose onthe wafer resulting in a local variation of the size of the imagedfeatures, often referred to as line width roughness (LWR). Speckle canbe reduced by stretching the pulse duration over a period of time or byincreasing the Etendue of the beam.

SUMMARY

Given the foregoing, what is needed is an improved method, apparatus,and system to provide a pulse modifier that increases both temporalpulse length and Etendue of an illumination beam.

Embodiments of the present invention include a pulse modifier with anadjustable Etendue comprising a beam splitter, a divergence opticalelement, and a first and second curved mirror. The beam splitterreceives an input pulse of radiation and divides the input pulse into afirst and a second pulse portion. The beam splitter directs the firstpulse portion towards a divergence optical element, which diverts thefirst pulse portion by an angle resulting in a divergence whereinEtendue is increased. The beam splitter directs the second pulse portionas a portion of the output beam. A first mirror and a second mirror,each with a radius of curvature, face each other with a predeterminedseparation and receive the diverted first pulse portion and redirect thefirst pulse portion along the diverted beam path. The optical path ofthe first pulse portion through the pulse modifier is longer than thatof the second pulse portion, resulting in a delay and stretching of theinput pulse.

Another embodiment of the present invention includes a pulse modifierwith an adjustable Etendue comprising a beam splitter, a divergenceoptical element, and a first and second curved mirror where the beamsplitter and divergence optical elements are combined into a singleelement. The divergence/beam splitter receives an input pulse ofradiation and divides the input pulse into a first and a second pulseportion and diverts the first pulse portion by an angle resulting in adivergence wherein Etendue is increased. The divergence/beam splitterdirects the second pulse portion as a portion of the output beam. Afirst mirror and a second mirror, each with a radius of curvature, faceeach other with a predetermined separation and receive the divertedfirst pulse portion and redirect the first pulse portion along a beampath. The optical path of the first pulse portion through the pulsemodifier is longer than that of the second pulse portion, resulting in adelay and stretching of the input pulse.

In yet another embodiment of the present invention a pulse modifiercomprises a first and second beam splitter, a first and seconddivergence optical element, and a first and second curved mirror. Thefirst divergence/beam splitter receives an input pulse of radiation anddivides the input pulse into a first and a second pulse portion,directing the second portion of the beam towards the second beamsplitter. The second beam splitter passes a fourth portion of the beamas at least a portion of the output beam. The first beam splitterredirects the first portion of the beam to a first divergence opticalelement that diverts the first pulse portion by an angle resulting in adivergence wherein Etendue is increased. The first divergence opticalelement is further produces a first beam path between the first andsecond reflecting devices where the first portion of the beam traversesbetween the first and second reflecting devices more than once. Thesecond beam splitter redirects a third portion of the beam to a seconddivergence optical element that diverts the third pulse portion by anangle resulting in a divergence wherein Etendue is increased. The seconddivergence optical element further produces a second beam path betweenthe first and second reflecting devices where the third portion of thebeam traverses between the first and second reflecting devices more thanonce. After traversing between the first and second reflecting devices aportion of the first portion of the beam is reflected by the first beamsplitter towards the second beam splitter while another portion of thefirst portion of the beam is passed through the first beam splitter.After traversing between the first and second reflecting devices aportion of the third portion of the beam is reflected by the second beamsplitter and exits the system as a portion of an output beam whileanother portion of the third portion of the beam is passed through thesecond beam splitter.

Embodiments of the present invention further include a lithographysystem with a pulse modifier. The lithography system consists of anillumination system to condition a radiation beam for illumination of apatterning device, wherein the illumination system contains a pulsemodifier. The pulse modifier includes a first and second beam splitter,a first and second divergence optical element, and a first and secondcurved mirror where the beam splitter and divergence optical elementsare combined into a single element. The first divergence/beam splitterreceives an input pulse of radiation and divides the input pulse into afirst and a second pulse portion, directing the second portion of thebeam towards the second divergence/beam splitter. The seconddivergence/beam splitter passes a fourth portion of the beam as at leasta portion of the output beam. The first divergence/beam splitter is alsoconfigured to tilt and redirect the first portion of the beam to producea first beam path between the first and second reflecting devices wherethe first portion of the beam traverses between the first and secondreflecting devices more than once. The second divergence/beam splittertilts and redirects a third portion of the beam to produce a second beampath between the first and second reflecting devices where the thirdportion of the beam traverses between the first and second reflectingdevices more than once. After traversing between the first and secondreflecting devices a portion of the first portion of the beam isreflected by the beam splitter towards the second beam splitter whileanother portion of the first portion of the beam is passed through thefirst beam splitter. After traversing between the first and secondreflecting devices a portion of the third portion of the beam isreflected by the beam splitter and exits the system as a portion of anoutput beam while another portion of the third portion of the beam ispassed through the beam splitter.

Further features and advantages of the invention, as well as thestructure and operation of various embodiments of the present invention,are described in detail below with reference to the accompanyingdrawings. It is noted that the invention is not limited to the specificembodiments described herein. Such embodiments are presented herein forillustrative purposes only. Additional embodiments will be apparent topersons skilled in the relevant art(s) based on the teachings containedherein.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the relevant art(s) to makeand use the invention.

FIG. 1A is an illustration of a reflective lithographic apparatus,according to an embodiment of the present invention.

FIG. 1B is an illustration of a transmissive lithographic apparatus,according to an embodiment of the present invention.

FIG. 2A is an illustration of an asymmetric pulse modifier using onebeam splitter and one divergence optical element, according to anembodiment of the present invention.

FIGS. 2B and 2C illustrate a cross section of an input beam to anasymmetric pulse modifier and a cross section of the correspondingoutput beam.

FIG. 3 is an illustration of an asymmetric pulse modifier using acombined divergence/beam splitter, according to an embodiment of thepresent invention.

FIG. 4A is an illustration of a symmetric pulse modifier using two beamsplitters and two divergence optical elements with multiple reflections,according to an embodiment of the present invention.

FIGS. 4B and 4C illustrate a cross section of an input beam to asymmetric pulse modifier and a cross section of a corresponding outputbeam, according to an embodiment of the present invention.

FIG. 5A is a three dimensional illustration of a symmetric pulsemodifier, according to an embodiment of the present invention.

FIG. 5B is a top view of a symmetric pulse modifier, according to anembodiment of the present invention.

FIG. 5C is a three dimensional illustration of a symmetric pulsemodifier, according to another embodiment of the present invention.

FIG. 5D is a top view of a symmetric pulse modifier, according toanother embodiment of the present invention.

FIG. 6 is an illustration of a symmetric pulse modifier using a combineddivergence/beam splitter, according to an embodiment of the presentinvention.

FIG. 7 is an illustration of two beam splitters oriented atapproximately 90 degrees from each other, according to an embodiment ofthe present invention.

FIGS. 8 and 9 are Zemax simulation examples of divergence of a pulse ina pulse modifier, according to an embodiment of the present invention.

The features and advantages of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements. The drawing in which an elementfirst appears is indicated by the leftmost digit(s) in the correspondingreference number.

DETAILED DESCRIPTION

Embodiments of the present invention are directed to a pulse modifierwith adjustable Etendue. This specification discloses one or moreembodiments that incorporate the features of the present invention. Thedisclosed embodiment(s) merely exemplify the invention. The scope of theinvention is not limited to the disclosed embodiment(s). The inventionis defined by the claims appended hereto.

The embodiment(s) described, and references in the specification to “oneembodiment,” “an embodiment,” “an example embodiment,” etc., indicatethat the embodiment(s) described can include a particular feature,structure, or characteristic, but every embodiment can not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases are not necessarily referring to the same embodiment.Further, when a particular feature, structure, or characteristic isdescribed in connection with an embodiment, it is understood that it iswithin the knowledge of one skilled in the art to effect such feature,structure, or characteristic in connection with other embodimentswhether or not explicitly described.

Embodiments of the present invention can be implemented in hardware,firmware, software, or any combination thereof. Embodiments of thepresent invention can also be implemented as instructions stored on amachine-readable medium, which can be read and executed by one or moreprocessors. A machine-readable medium can include any mechanism forstoring or transmitting information in a form readable by a machine(e.g., a computing device). For example, a machine-readable medium caninclude the following: read-only memory (ROM); random access memory(RAM); magnetic disk storage media; optical storage media; and, flashmemory devices. Further, firmware, software, routines, instructions canbe described herein as performing certain actions. However, it should beappreciated that such descriptions are merely for convenience and thatsuch actions in fact result from computing devices, processors,controllers, or other devices executing the firmware, software,routines, instructions, etc.

FIG. 1 is an illustration of a lithographic apparatus 100 andlithographic apparatus 100′, respectively, in which embodiments of thepresent invention can be implemented. Lithographic apparatus 100 andlithographic apparatus 100′ each include the following: an illuminationsystem (illuminator) IL configured to condition a radiation beam B(e.g., DUV or EUV radiation); a support structure (e.g., a mask table)MT configured to support a patterning device (e.g., a mask, a reticle,or a dynamic patterning device) MA and connected to a first positionerPM configured to accurately position the patterning device MA; and, asubstrate table (e.g., a wafer table) WT configured to hold a substrate(e.g., a resist coated wafer) W and connected to a second positioner PWconfigured to accurately position the substrate W. Lithographicapparatuses 100 and 100′ also have a projection system PS configured toproject a pattern imparted to the radiation beam B by patterning deviceMA onto a target portion (e.g., comprising one or more dies) C of thesubstrate W. In lithographic apparatus 100, the patterning device MA andthe projection system PS are reflective. In lithographic apparatus 100′,the patterning device MA and the projection system PS are transmissive.

The illumination system IL can include various types of opticalcomponents, such as refractive, reflective, magnetic, electromagnetic,electrostatic or other types of optical components, or any combinationthereof, for directing, shaping, or controlling the radiation B.

The support structure MT holds the patterning device MA in a manner thatdepends on the orientation of the patterning device MA, the design ofthe lithographic apparatuses 100 and 100′, and other conditions, such asfor example whether or not the patterning device MA is held in a vacuumenvironment. The support structure MT can use mechanical, vacuum,electrostatic, or other clamping techniques to hold the patterningdevice MA. The support structure MT can be a frame or a table, forexample, which can be fixed or movable, as required. The supportstructure MT can ensure that the patterning device is at a desiredposition, for example, with respect to the projection system PS.

The term “patterning device” MA should be broadly interpreted asreferring to any device that can be used to impart a radiation beam Bwith a pattern in its cross-section, such as to create a pattern in thetarget portion C of the substrate W. The pattern imparted to theradiation beam B can correspond to a particular functional layer in adevice being created in the target portion C, such as an integratedcircuit.

The patterning device MA can be transmissive (as in lithographicapparatus 100′ of FIG. 1B) or reflective (as in lithographic apparatus100 of FIG. 1A). Examples of patterning devices MA include reticles,masks, programmable mirror arrays, and programmable LCD panels. Masksare well known in lithography, and include mask types such as binary,alternating phase shift, and attenuated phase shift, as well as varioushybrid mask types. An example of a programmable mirror array employs amatrix arrangement of small mirrors, each of which can be individuallytilted so as to reflect an incoming radiation beam in differentdirections. The tilted mirrors impart a pattern in the radiation beam Bwhich is reflected by the mirror matrix.

The term “projection system” PS can encompass any type of projectionsystem, including refractive, reflective, catadioptric, magnetic,electromagnetic and electrostatic optical systems, or any combinationthereof, as appropriate for the exposure radiation being used, or forother factors, such as the use of an immersion liquid or the use of avacuum. A vacuum environment can be used for EUV or electron beamradiation since other gases can absorb too much radiation or electrons.A vacuum environment can therefore be provided to the whole beam pathwith the aid of a vacuum wall and vacuum pumps.

Lithographic apparatus 100 and/or lithographic apparatus 100′ can be ofa type having two (dual stage) or more substrate tables (and/or two ormore mask tables) WT. In such “multiple stage” machines, the additionalsubstrate tables WT can be used in parallel, or preparatory steps can becarried out on one or more tables while one or more other substratetables WT are being used for exposure.

Referring to FIGS. 1A and 1B, the illuminator IL receives a radiationbeam from a radiation source SO. The source SO and the lithographicapparatuses 100, 100′ can be separate entities, for example, when thesource SO is an excimer laser. In such cases, the source SO is notconsidered to form part of the lithographic apparatuses 100 or 100′, andthe radiation beam B passes from the source SO to the illuminator ILwith the aid of a beam delivery system BD (in FIG. 1B) including, forexample, suitable directing mirrors and/or a beam expander. In othercases, the source SO can be an integral part of the lithographicapparatuses 100, 100′—for example when the source SO is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD, if required, can be referred to as a radiation system.

The illuminator IL can include an adjuster AD (in FIG. 1B) for adjustingthe angular intensity distribution of the radiation beam. Generally, atleast the outer and/or inner radial extent (commonly referred to as“σ-outer” and “σ-inner,” respectively) of the intensity distribution ina pupil plane of the illuminator can be adjusted. In addition, theilluminator IL can comprise various other components (in FIG. 1B), suchas an integrator IN and a condenser CO. The illuminator IL can be usedto condition the radiation beam B to have a desired uniformity andintensity distribution in its cross section.

Referring to FIG. 1A, the radiation beam B is incident on the patterningdevice (e.g., mask) MA, which is held on the support structure (e.g.,mask table) MT, and is patterned by the patterning device MA. Inlithographic apparatus 100, the radiation beam B is reflected from thepatterning device (e.g., mask) MA. After being reflected from thepatterning device (e.g., mask) MA, the radiation beam B passes throughthe projection system PS, which focuses the radiation beam B onto atarget portion C of the substrate W. With the aid of the secondpositioner PW and position sensor IF2 (e.g., an interferometric device,linear encoder, or capacitive sensor), the substrate table WT can bemoved accurately (e.g., so as to position different target portions C inthe path of the radiation beam B). Similarly, the first positioner PMand another position sensor IF1 can be used to accurately position thepatterning device (e.g., mask) MA with respect to the path of theradiation beam B. Patterning device (e.g., mask) MA and substrate W canbe aligned using mask alignment marks M1, M2 and substrate alignmentmarks P1, P2.

Referring to FIG. 1B, the radiation beam B is incident on the patterningdevice (e.g., mask MA), which is held on the support structure (e.g.,mask table MT), and is patterned by the patterning device. Havingtraversed the mask MA, the radiation beam B passes through theprojection system PS, which focuses the beam onto a target portion C ofthe substrate W. With the aid of the second positioner PW and positionsensor IF (e.g., an interferometric device, linear encoder, orcapacitive sensor), the substrate table WT can be moved accurately(e.g., so as to position different target portions C in the path of theradiation beam B). Similarly, the first positioner PM and anotherposition sensor (not shown in FIG. 1B) can be used to accuratelyposition the mask MA with respect to the path of the radiation beam B(e.g., after mechanical retrieval from a mask library or during a scan).

In general, movement of the mask table MT can be realized with the aidof a long-stroke module (coarse positioning) and a short-stroke module(fine positioning), which form part of the first positioner PM.Similarly, movement of the substrate table WT can be realized using along-stroke module and a short-stroke module, which form part of thesecond positioner PW. In the case of a stepper (as opposed to a scanner)the mask table MT can be connected to a short-stroke actuator only orcan be fixed. Mask MA and substrate W can be aligned using maskalignment marks M1, M2 and substrate alignment marks P1, P2. Althoughthe substrate alignment marks (as illustrated) occupy dedicated targetportions, they can be located in spaces between target portions (knownas scribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the mask MA, the mask alignment marks can belocated between the dies.

The lithographic apparatuses 100 and 100′ can be used in at least one ofthe following modes:

1. In step mode, the support structure (e.g., mask table) MT and thesubstrate table WT are kept essentially stationary, while an entirepattern imparted to the radiation beam B is projected onto a targetportion C at one time (i.e., a single static exposure). The substratetable WT is then shifted in the X and/or Y direction so that a differenttarget portion C can be exposed.

2. In scan mode, the support structure (e.g., mask table) MT and thesubstrate table WT are scanned synchronously while a pattern imparted tothe radiation beam B is projected onto a target portion C (i.e., asingle dynamic exposure). The velocity and direction of the substratetable WT relative to the support structure (e.g., mask table) MT can bedetermined by the (de-)magnification and image reversal characteristicsof the projection system PS.

3. In another mode, the support structure (e.g., mask table) MT is keptsubstantially stationary holding a programmable patterning device, andthe substrate table WT is moved or scanned while a pattern imparted tothe radiation beam B is projected onto a target portion C. A pulsedradiation source SO can be employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizes aprogrammable patterning device, such as a programmable mirror array of atype as referred to herein.

Combinations and/or variations on the described modes of use or entirelydifferent modes of use can also be employed.

Although specific reference can be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein can haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), and thin-filmmagnetic heads. The skilled artisan will appreciate that, in the contextof such alternative applications, any use of the terms “wafer” or “die”herein can be considered as synonymous with the more general terms“substrate” or “target portion,” respectively. The substrate referred toherein can be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool, and/or an inspectiontool. Where applicable, the disclosure herein can be applied to such andother substrate processing tools. Further, the substrate can beprocessed more than once, for example, in order to create a multi-layerIC, so that the term substrate used herein can also refer to a substratethat already contains multiple processed layers.

In a further embodiment, lithographic apparatus 100 includes an extremeultraviolet (EUV) source, which is configured to generate a beam of EUVradiation for EUV lithography. In general, the EUV source is configuredin a radiation system (see below), and a corresponding illuminationsystem is configured to condition the EUV radiation beam of the EUVsource.

In the embodiments described herein, the terms “lens” and “lenselement,” where the context allows, can refer to any one or combinationof various types of optical components, including refractive,reflective, magnetic, electromagnetic, and electrostatic opticalcomponents.

Further, the terms “radiation” and “beam” used herein encompass alltypes of electromagnetic radiation, including ultraviolet (UV) radiation(e.g., having a wavelength λ of 365, 248, 193, 157 or 126 nm), extremeultraviolet (EUV or soft X-ray) radiation (e.g., having a wavelength inthe range of 5-20 nm such as, for example, 13.5 nm), or hard X-rayworking at less than 5 nm, as well as particle beams, such as ion beamsor electron beams. Generally, radiation having wavelengths between about780-3000 nm (or larger) is considered IR radiation. UV refers toradiation with wavelengths of approximately 100-400 nm. Withinlithography, the term “UV” also applies to the wavelengths that can beproduced by a mercury discharge lamp: G-line 436 nm; H-line 405 nm;and/or, I-line 365 nm. Vacuum UV, or VUV (i.e., UV absorbed by air),refers to radiation having a wavelength of approximately 100-200 nm.Deep UV (DUV) generally refers to radiation having wavelengths rangingfrom 126 nm to 428 nm, and in an embodiment, an excimer laser cangenerate DUV radiation used within a lithographic apparatus. It shouldbe appreciated that radiation having a wavelength in the range of, forexample, 5-20 nm relates to radiation with a certain wavelength band, ofwhich at least part is in the range of 5-20 nm.

FIG. 2A is an illustration of a beam modifier 200 (e.g., an asymmetricbeam modifier with adjustable Etendue), according to an embodiment ofthe invention.

In this example, beam modifier 200 includes a beam splitter 210, adivergence optical element 230, and first and second curved reflectingdevices 240 and 242.

In one example, the following beam path or cycle is traversed by atleast one beam of radiation entering beam modifier 200. Input pulse 201Aenters asymmetric beam modifier 200 along beam path 205. For example, anexample waveshape is shown graphed as 201-In Graph. Input pulse 201A isdivided by beam splitter 210 into two pulse portions including reflectedpulse portion 201B and transmitted pulse portion 201C. Portion 201Cexits asymmetric beam modifier 200 as a portion of output beam201-Output. Portion 201B travels along beam path 211 towards divergenceoptical element 230. Divergence optical element 230, e.g., an opticalwedge, diverges (e.g. tilts) portion 201B so that portion 201B travelsalong beam path 212, diverging from beam path 211 by angle 235. An angleof divergence from path 211 depends on an angle of divergence opticalelement 230. Portion 201D reflects from mirror 240 to travel along beampath 213. Mirror 242 reflects portion 201D to travel along beam path 214to first mirror 240. Portion 201D reflects from mirror 240 to travelalong beam path 215 to mirror 242. Portion 201D reflects from mirror 242and travels back to beam splitter 210 along beam path 216. Portion 201Dis divided by beam splitter 210. The reflected part of portion 201Dagain forms part of 201-Output.

In this example, portion 201D is delayed in time because it travelsalong a longer beam path than portion 201C. Also, the reflected part ofportion 201D added to 201-Output has lower intensity than 201C pulseportion.

In one example, the transmitted part of portion 201D can then repeat thecycle. In each cycle pass divergence optical element 230 further tiltsthe beam.

In this embodiment, as there is only a single divergence optical element230, and therefore 201-Output is asymmetric.

The reflective surfaces of two curved mirrors 240 and 242 face eachother. The curved mirrors are separated by a predetermined distance orseparation, for example the distance or separation can be approximatelyequal to the radius of curvature of each curved mirror. For example,curved mirrors 240 and 242 form a confocal mirror with a radius ofcurvature of 2d, where d is the separation distance between mirrors 240and 242. In one example, curved mirrors 240 and 242 are configured toreimage a portion of the beam at beam splitter 210.

In one example, beam splitter 210 can be configured to any desired ratioof reflection to transmission. For example, when using a 60R/40T (60%reflection and 40% transmissions) beam splitter 210 with negligibleloss, portion 201B represents 60% of input pulse 201A, while portion201C represents 40% of input pulse 201A. In this example, 201-Ouput isproduced from a series of time delayed, intensity reduced, and tiltedseries of pulses. After a first cycle, portion 201C is about 60% of theintensity of input pulse 201A. After an optional second cycle,201-Output is about 24% of the of the intensity of original input pulse201A. Similarly, a third cycle generates about 9.6%, a fourth cyclegenerates about 3.9%, and a fifth cycle generates about 1.5% of theoriginal intensity of 201A. Therefore, after a certain number of pulses,the intensity of 201A can completely dissipate.

In one example, a time delay between the pulses which constitute201-Output is based on path length of beam paths 211, 212, 213, 214, 215and 216. Some of the beam paths are defined by the separation betweenmirrors 240 and 242. The separation can be designed to allow foroverlapping, adjacent, or separated output pulses. The result of suchtime delays between the pulses that are used to produce 201-Output is aincrease in the temporal pulse of an illumination beam.

A relative intensity of the output pulses with respect to the inputpulse and with respect to each other is influenced by thereflection/transmission ratio of beam splitter 210. A degree ofdivergence is a function of the degree of tilt in the divergence opticalelement, which can also be adjusted.

FIG. 2B illustrates a shape of an input pulse, such as input pulse 201A,according to an embodiment of the present invention.

FIG. 2C illustrates a shape of a corresponding output beam, such as201-Output, with an asymmetrical divergence shown on the right side ofthe Output Pulses, according to an embodiment of the invention. In thismanner, the divergence of the beam is increased without decreasing thebeam size, thus increasing the Etendue.

In lithography, speckle is a function of both the pulse duration and theEtendue of the beam. Therefore, by increasing the time delay betweenoutput pulses, as well as the Etendue, as described in the aboveembodiment, speckle can be substantially reduced and/or eliminated bystretching the pulse duration over a period of time and/or by increasingthe Etendue of the beam.

FIG. 3 is an illustration of a beam modifier 300, according to anembodiment of the invention. For example, beam modifier 300 can be anasymmetric beam modifier with adjustable Etendue using a combined beamsplitter and divergence optical element 325. Beam modifier 300 operatessimilarly to beam modifier 200 in the embodiment shown in FIG. 2.However, a beam splitter function is combined with the divergencefunction through element 325. Beam modifier 300 also includes reflectingdevices 340 and 342.

In one example, an cycle of a beam traveling through beam modifierincludes input pulse 301A traveling along beam path 305, which isdivided and diverged by element 325. Input pulse 301A is divided intotwo pulse portions consisting of diverged and reflected pulse portion301D and transmitted pulse portion 301C. Element 325 tilts the reflectedpulse portion of input pulse 301A to generate a diverged and reflectedportion 301D, which is tilted by an angle 315 along beam path 311.Portion 301D reflects from mirror 340, travels along beam path 313,reflects from mirror 342, travels along beam path 314, reflects frommirror 340, travels along beam path 315, reflects from mirror 342, andtravels back to element splitter 325. Portion 301D is again divided byelement 325. The reflected part of portion 301D again forms part of to301-Output. In one example, the transmitted part of portion 301D repeatsthe cycle, and further contributes to 301-Output.

As discussed above, as portion 301D travels along a longer beam paththan pulse portion 301C, pulse portion 301D is delayed in time. Also, asdescribed above, as the reflected part of portion 301D is again split byelement 325, the reflected part of portion 301D that is added to301-Output has a lower intensity than portion 301C. As further discussedabove, after a certain number of cycles, the original energy of pulse301A is substantially completely dissipated.

In this embodiment, as there is only a single element 325, the301-Output is asymmetric. These attributes will not be repeated forsystems discussed below, although a skilled artisan will understand thatany systems discussed below can also have these attributes.

In one example, a beam splitting functionality of element 325 can beconfigured to any desired ratio of reflection to transmission. If, forexample, a 60R/40T (60% reflection and 40% transmissions) beam splittingcharacteristic is used for element 325, and assuming negligible loss atelement 325, portion 301D represents 60% of input pulse 301A, whiletransmitted pulse portion 301C represents 40% of input pulse 301A. Theseattributes will not be repeated for systems discussed below, although askilled artisan will understand that any systems discussed below canalso have these attributes.

FIG. 4A is an illustration of a beam modifier 400 (e.g., a symmetricbeam modifier with adjustable Etendue), according to an embodiment ofthe invention.

In this example, beam modifier 400 includes first and second beamsplitters 410 and 430, first and second divergence optional elements 420and 430, and first and second curved reflecting devices 440 and 442.

In one example, the following beam path or cycle is traversed by atleast one beam of radiation entering beam modifier 400. Input pulse 401Aenters symmetric beam modifier 400 along beam path 405. Input pulse 401Ais divided by first beam splitter 410 into two pulse portions includingreflected pulse portion 401B and transmitted pulse portion 401C. Portion401C travels along beam path 417 to the second beam splitter 430, whereportion 401C is divided into a reflected pulse portion, pulse portion401E, and a transmitted pulse portion, pulse portion 401F. Portion 401Fexits symmetric beam modifier 400 as a portion of output beam401-Output.

In this example, input pulse 401A is divided by both first and secondbeam splitters, 410 and 430, to travel two sets of independent beampaths which can exist in separate planes. The first division of inputpulse 401A is accomplished by first beam splitter 410, and diverged ofportion 401B is performed by first divergence optical element 420, suchthat portion 401B travels along beam paths 411, 412, 413, 414, 415, and416. The second division of beam 401A is portion 401C, which isaccomplished by second beam splitter 430, and diverged of portion 401Eis performed by second divergence optical element 445, and portion 401Etravels along beam paths 431, 432, 433, 434, 435, and 436.

In this example, portion 401B travels along beam path 411 towards firstdivergence optical element 420. Divergence optical element 420, e.g., anoptical wedge, diverges (e.g., tilts) portion 401B so that portion 401Btravels along beam path 412, diverging from beam path 411 by angle 425.An angle of divergence from path 411 depends on an angle of divergenceoptical element 420. Portion 401D reflects from mirror 440 to travelalong beam path 413. Mirror 442 reflects portion 401D to travel alongbeam path 414 to mirror 440. Portion 401D reflects from mirror 440 totravel along beam path 415 to mirror 442. Portion 401D reflects frommirror 442 and travels along beam path 416 back to first beam splitter410. Portion 401D is further divided by first beam splitter 410, so thata reflected portion is directed along beam path 417 to second beamsplitter 430 and a transmitted portion travels on path 411 for anoptional additional cycle pass.

In this example, portion 401D is delayed in time because it travelsalong a longer beam path than portion 401C. Also, the reflected part ofportion 401D that travels to second beam splitter 430 has lowerintensity than portion 401C.

In one example, the transmitted part of portion 401D can then repeat thecycle. In each cycle pass, divergence optical element 420 further tiltsthe beam in addition to the delay associated with the beam paths.

After the first cycle, or optional additional cycles, transmitted pulseportion 401C of input pulse portion 401A travels along beam path 417 tosecond beam splitter 430 where it is divided into two pulse portionsincluding reflected pulse portion 401E and transmitted pulse portion401F. Portion 401F exits symmetric beam modifier 400 as a portion ofoutput beam 401-Output.

Also, in this example, portion 401E travels along beam path 431 towardssecond divergence optical element 445. Second divergence optical element445, e.g., an optical wedge, diverges (e.g., tilts) portion 401E so thatportion 401E travels along beam path 432. An angle of divergence frompath 431 depends on an angle of second divergence optical element 445.Portion 401E reflects from mirror 442 to travel along beam path 433.Mirror 440 reflects portion 401E to travel along beam path 434 to mirror442. Portion 401E reflects from mirror 442 to travel along beam path 435to mirror 440. Portion 401E reflects from mirror 440 and travels alongbeam path 436 back to second beam splitter 430. Portion 401E is furtherdivided by second beam splitter 430, such that a reflected portion isdirected along beam path 450 as a portion of output beam 401-Output anda transmitted portion travels on path 417 for a optional additionalcycle pass.

In this example, portion 401E is delayed in time because it travelsalong a longer beam path than portion 401F. Also, the reflected part ofportion 401E that exits has lower intensity than 401F pulse portion.

In one example, the transmitted part of portion 401E can then repeat thecycle. In each cycle pass, second divergence optical element 445 furthertilts the beam in addition to the delay associated with the beam paths.

In one example, the reflective surfaces of two curved mirrors 440 and442 face each other. The curved mirrors are separated by a predetermineddistance or separation, for example the distance or separation can beapproximately equal to the radius of curvature of each curved mirror.For example, curved mirrors 440 and 442 form a confocal mirror with aradius of curvature of 2d, where d is the separation distance betweenmirrors 440 and 442.

As the embodiment in FIG. 4 consists of two sets of beam splitters anddivergence optical elements, such splitters and optical elements can bepositioned such that the output beam of FIG. 4, 401-Output, issymmetric.

FIG. 4B illustrates a shape of an input pulse, such as input pulse 401A,according to an embodiment of the present invention.

FIG. 4C illustrates a shape of a corresponding output beam, such as401-Output, with a symmetric output divergence shown on both the leftand right side of the Output Pulses, according to an embodiment of theinvention. In this manner the divergence of the beam is increasedwithout decreasing the beam size, thus increasing the Etendue.

In other embodiments, additional beam splitters and divergence opticalelements can be configured to increase the divergence and Etendue inother planes, such that the increased divergence can occur in both thehorizontal direction, as shown in FIG. 4C, but also in a verticaldirection. There is no limitation on the number or positions of beamsplitters and divergence optical elements that can be used to modify abeam with increased Etendue.

FIGS. 5A and 5B are three dimensional illustrations of a beam modifier500, according to an embodiment of the present invention. For example,beam modifier 500 can be a symmetric beam modifier with adjustableEtendue. Beam modifier 500 operates similarly to beam modifier 400 inthe embodiment shown in FIG. 4. However, in this embodiment the planesof the beam paths from the beam splitters are symmetric.

In this example, beam modifier 500 includes two beam splitters, 510 and530, two divergence optical elements 520 and 545, and two mirrors, 540and 542.

An input pulse travels along beam path 505 before being divided by firstbeam splitter 510. A reflected portion of the beam is diverged by firstdivergence optical element 520 to travel along beam path 511. Atransmitted potion of the beam travels to second beam splitter 530.Based on beam splitter 530, a reflected portion is diverged by seconddivergence optical element 545 along beam path 512, and a transmittedportion exits along beam path 550.

FIG. 5B illustrates a top view of this embodiment shown in FIG. 5 a,which shows beam paths 511 and 512 existing in perpendicular planes.

In further embodiments, additional beam splitters and divergence opticalelements can be added to generate additional planes of beam paths, whichare all ultimately directed to the output beam along beam path 550.

FIGS. 5C and 5D illustrate a beam modifier 500′, according to anembodiment of the present invention. For example, beam modifier 500′ canbe a symmetric beam modifier with adjustable Etendue. Beam modifier 500′operates similarly to beam modifier 500 in the embodiment shown in FIGS.5A and 5B. However, in this embodiment the divergence optical elementsare replaced by parallel plate optical elements.

In this example, beam modifier 500′ includes two beam splitters 510 and530, two parallel plate optical elements 522 and 547, and two mirrors540 and 542.

An input pulse travels along beam path 505 before being divided by firstbeam splitter 510. A reflected portion of the beam is shifted by firstparallel plate optical element 522 to travel along beam path 511. Atransmitted potion of the beam travels to second beam splitter 530.Based on beam splitter 530, a reflected portion is shifted by secondparallel plate optical element 547 along beam path 512, and atransmitted portion exits along beam path 550. Parallel plate opticalelements 522 and 547 are tilted about an axis perpendicular to the beampropagation direction so that the size of the beam is increased withoutmodifying the divergence of the beam, thus increasing the Etendue of thebeam.

FIG. 5D illustrates a top view of the embodiment shown in FIG. 5C, whichshows beam paths 511 and 512 existing in perpendicular planes.

In further embodiments, additional beam splitters and parallel plateoptical elements can be added to generate additional planes of beampaths, which are all ultimately directed to the output beam along beampath 550.

In another embodiment, parallel plate optical element 522 is combinedwith beam splitter 510 to form a relatively thicker beam splitter toaccomplish the same result.

FIG. 6 is an illustration of a beam modifier 600, according to anembodiment of the invention. For example, beam modifier 600 can be asymmetric beam modifier with adjustable Etendue using a combined beamsplitter and divergence optical element. Beam modifier 600 operatessimilarly to beam modifier 400 in the embodiment shown in FIG. 4.However, a beam splitter function is combined with the divergencefunction, similar to as described for the embodiment of FIG. 3.

In this example, beam modifier 600 includes first and seconddivergence/beam splitting elements 625 and 627, and first and secondcurved reflecting devices 640 and 642.

In one example, the following beam path or cycle is traversed by atleast one beam of radiation entering beam modifier 600. Input pulse 601Aenters beam modifier 600 along beam path 605. Input pulse 601A isdivided into two pulse portions consisting of diverged and reflectedpulse portion 601D and transmitted pulse portion 601C. Portion 601Ctravels along beam path 617 to second divergence/beam splitting element627, such that portion 601C is divided into a reflected pulse portion601E and a transmitted pulse portion 601F. Portion 601F exits symmetricbeam modifier 600 as a portion of output beam 601-Output.

In this example, element 625 tilts the reflected pulse portion of inputpulse 601A to generate a diverged and reflected portion 601D, which istilted by an angle 615 along beam path 611. Portion 601D reflects frommirror 640 to travel along beam path 613. Mirror 642 reflects portion601D to travel along beam path 614 to mirror 640. Portion 601D reflectsfrom mirror 640 to travel along beam path 615 to mirror 642. Portion601D reflects from mirror 642 and travels along beam path 616 back toelement 625. Portion 601D is further divided by element 625, such that areflected portion of split portion 601D is directed along beam path 617to element 627 and a transmitted portion of portion 601D travels on path611 for another cycle pass.

In this example, portion 601D is delayed in time because it travelsalong a longer beam path than portion 601C. Also, the reflected part ofportion 601D that travels to element 627 has lower intensity than 601Cpulse portion.

In one example, the transmitted part of portion 601D can then repeat thecycle. In each cycle pass, element 625 further tilts the beam inaddition to the delay associated with the beam paths.

In this example, transmitted pulse portion 601C of input pulse portion601A travels along beam path 617 to element 627, where it is dividedinto two pulse portions including reflected and diverged pulse portion601E and transmitted pulse portion 601F. Portion 601F exits symmetricbeam modifier 600 as a portion of output beam 601-Output.

Element 627 tilts the reflected pulse portion of pulse portion 601C togenerate a diverged and reflected portion 601E, which is tilted by anangle 645 along beam path 631. Portion 601E reflects from mirror 642 totravel along beam path 633. Portion 601E reflects from mirror 642 totravel along beam path 633. Mirror 640 reflects portion 601E to travelalong beam path 634 to mirror 642. Portion 401E reflects from mirror 642to travel along beam path 635 to mirror 640. Portion 601E reflects frommirror 640 and travels back to second divergence/beam splitter 627 alongbeam path 636. Portion 401E is further divided by element 627, where areflected portion is directed along beam path 650 as a portion of outputbeam 601-Output and the transmitted portion travels on path 617 foranother cycle pass.

In this example, portion 601E is delayed in time because it travelsalong a longer beam path than portion 601F. Also, the reflected part ofportion 601E that exits has lower intensity than 601F pulse portion.

In one example, the transmitted part of portion 601E can then repeat thecycle. In each cycle pass, element 627 further tilts the beam inaddition to the delay associated with the beam paths.

In this example, the reflective surfaces of two curved mirrors 640 and642 face each other. The curved mirrors are separated by a predetermineddistance or separation, for example the distance or separation can beapproximately equal to the radius of curvature of each curved mirror.For example, curved mirrors 640 and 642 form a confocal mirror with aradius of curvature of 2d, where d is the separation distance betweenmirrors 640 and 642.

FIG. 7 is an illustration of a dual beam splitter 700 (e.g., which canbe included in a symmetric beam modifier with adjustable Etendue),according to an embodiment of the invention.

In this example, dual beam splitter 700 includes first beam splitter 725and second beam splitter 727. In another example, these elements 720 and725 can be splitter/divergence elements, as discussed above.

In one example, there can be a positional shift in a beam passingthrough elements 725 and 727 because of a finite thickness of theelements. This is illustrated as path 716 between paths 705 and 717.However, through orienting element 727 approximately perpendicular toelement 725, the shift is substantially corrected through beam shift718, which shifts the beam path between path 717 and 750.

FIGS. 8 and 9 illustrate a Zemax simulation example 800 and 900,according to an embodiment of the present invention.

FIG. 8 illustrates an initial Zemax simulation 800 using the embodimentillustrated in FIG. 4 of a symmetric beam modifier. A tilt angle of thedivergence optical elements is set to about 0.00 degrees and delivers adivergence of approximately 1 mrad.

FIG. 9 illustrates simulation 900, which shows a difference resultingfrom increasing a tilt angle of the divergence optical elements toapproximately 0.04 degrees. The divergence is increased to approximately2.7 mrad. Therefore, by adjusting the amount of divergence angle in eachdivergence optical element, and adjusting the transmission amounts ofthe beam splitters, a desired divergence profile can be achieved whereEtendue is increased without decreasing the size of the beam.

CONCLUSION

It is to be appreciated that the Detailed Description section, and notthe Summary and Abstract sections, is intended to be used to interpretthe claims. The Summary and Abstract sections can set forth one or morebut not all exemplary embodiments of the present invention ascontemplated by the inventor(s), and thus, are not intended to limit thepresent invention and the appended claims in any way.

The present invention has been described above with the aid offunctional building blocks illustrating the implementation of specifiedfunctions and relationships thereof. The boundaries of these functionalbuilding blocks have been arbitrarily defined herein for the convenienceof the description. Alternate boundaries can be defined so long as thespecified functions and relationships thereof are appropriatelyperformed.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent invention. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

The breadth and scope of the present invention should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

What is claimed is:
 1. A system, comprising: first and second curvedreflecting devices; a beam splitter; and a parallel plate opticalelement, wherein the beam splitter and the parallel plate opticalelement are combined into a single element and the single element isconfigured to: reflect and shift a first portion of a beam that begins acycle during which the beam travels through the system, and transmit asecond portion of the beam to generate at least a portion of an outputbeam, wherein during the cycle the combined beam splitter and parallelplate optical element directs the first portion of the beam along a beampath between the first and second reflecting devices, such that thefirst portion of the beam traverses between the first and secondreflecting devices more than once, and wherein the cycle ends aftertraversal between the first and second reflecting devices, such that afirst part of the first portion of the beam is reflected by the beamsplitter and exits the system to generate another portion of the outputbeam and a second part of the first portion of the beam is transmittedthrough the combined beam splitter and parallel plate optical element torepeat the cycle.
 2. The system of claim 1, wherein: a first segment ofthe cycle comprises a beam path from the first reflecting device to thesecond reflecting device; a second segment of the cycle comprises a beampath from the second curved reflecting device to the first curvedreflecting device; a third segment of the cycle comprises a beam pathfrom the first curved reflecting device to the second curved reflectingdevice; and a fourth segment of the cycle comprises a beam path from thesecond curved reflecting device to the combined beam splitter andparallel plate optical element.
 3. The system of claim 1, wherein thefirst and second curved reflecting devices comprise a confocal mirror.4. The system of claim 1, wherein the parallel plate optical element isconfigured to increase beam size of the first portion of the beam whilemaintaining a constant divergence to increase Etendue of the outputbeam.
 5. A lithographic system, comprising: an illumination systemconfigured to condition a radiation beam being provided for illuminationof a patterning device, the illumination system comprising a pulsemodifier that comprises: first and second curved mirrors; a beamsplitter; and a parallel plate optical element, wherein the beamsplitter and the parallel plate optical element are combined into asingle element and the single element is configured to: reflect andshift a first pulse portion of a pulse of radiation that begins a cycleduring which the pulse of radiation travels through the illuminationsystem, and transmit a second pulse portion of the pulse of radiation togenerate at least a portion of an output beam, wherein during the cyclethe combined beam splitter and parallel plate optical element directsthe first pulse portion of the pulse of radiation along a beam pathbetween the first and second curved mirrors, such that the first pulseportion of the pulse of radiation traverses between the first and secondcurved mirrors more than once, wherein the cycle ends after traversalbetween the first and second curved mirrors, such that a first part ofthe first pulse portion of the pulse of radiation is reflected by thebeam splitter and exits the illumination system to generate anotherportion of the output beam and a second part of the first pulse portionof the pulse of radiation is transmitted through the combined beamsplitter and parallel plate optical element to repeat the cycle, andwherein the pulse modifier is configured to increase Etendue of theoutput beam.
 6. The lithographic system of claim 5, wherein: a firstsegment of the cycle comprises a beam path from the first curved mirrorto the second curved mirror; a second segment of the cycle comprises abeam path from the second curved mirror to the first curved mirror; athird segment of the cycle comprises a beam path from the first curvedminor to the second curved mirror; and a fourth segment of the cyclecomprises a beam path from the second curved mirror to the combined beamsplitter and parallel plate optical element.
 7. The lithographic systemof claim 5, wherein the first and second curved mirrors comprise aconfocal mirror.
 8. The lithographic system of claim 5, wherein theparallel plate optical element is configured to increase pulse size ofthe first pulse portion of the pulse of radiation while maintaining aconstant divergence to increase Etendue of the output beam.
 9. A methodof modifying a pulse of radiation to increase Etendue of an illuminationbeam in a lithographic system, the method comprising: providing firstand second curved mirrors; providing a beam splitter; providing aparallel plate optical element; combining the beam splitter and theparallel plate optical element into a single element; reflecting, usingthe single element, a first pulse portion of the pulse of radiation;shifting, using the single element, the first pulse portion of the pulseof radiation; beginning a cycle during which the pulse of radiationtravels through the illumination system; transmitting, using the singleelement, a second pulse portion of the pulse of radiation to generate atleast a portion of an output beam; directing, using the single element,the first pulse portion of the pulse of radiation along a beam pathbetween the first and second curved mirrors during the cycle, such thatthe first pulse portion of the pulse of radiation traverses between thefirst and second curved mirrors more than once; reflecting, using thesingle element, a first part of the first pulse portion of the pulse ofradiation; generating another portion of the output beam by exiting thefirst part of the first pulse portion of the pulse of radiation from theillumination system; and transmitting, using the single element, asecond part of the first pulse portion of the pulse of radiation torepeat the cycle, wherein the cycle ends after traversal between thefirst and second curved mirrors, such that the first part of the firstpulse portion of the pulse of radiation is reflected, the first part ofthe first pulse portion exits the illumination system, and the secondpart of the first pulse portion of the pulse of radiation istransmitted.
 10. The method of modifying a pulse of radiation of claim9, wherein beginning a cycle during which the pulse of radiation travelsthrough the illumination system further comprises: enabling a beam pathfrom the first curved mirror to the second curved mirror to create afirst segment of the cycle; enabling a beam path from the second curvedmirror to the first curved mirror to create a second segment of thecycle; enabling a beam path from the first curved mirror to the secondcurved mirror to create a third segment of the cycle; and enabling abeam path from the second curved mirror to the single element to createa fourth segment of the cycle.
 11. The method of modifying a pulse ofradiation of claim 9, wherein providing first and second curved mirrorsfurther comprises: providing a first confocal mirror for the firstcurved mirror; and providing a second confocal mirror for the secondcurved mirror.
 12. The method of modifying a pulse of radiation of claim9, further comprising: increasing pulse size of the first pulse portionof the pulse of radiation by using the parallel plate optical elementwhile maintaining a constant divergence to increase Etendue of theoutput beam.
 13. A method of modifying a beam in a system, the methodcomprising: providing first and second curved reflecting devices;providing a beam splitter; and providing a parallel plate opticalelement; combining the beam splitter and the parallel plate opticalelement into a single element; reflecting, using the single element, afirst portion of a beam; shifting, using the single element, the firstportion of the beam; beginning a cycle during which the beam travelsthrough the system; transmitting, using the single element, a secondportion of the beam to generate at least a portion of an output beam;directing, using the single element, the first portion of the beam alonga beam path between the first and second reflecting devices during thecycle, such that the first portion of the beam traverses between thefirst and second reflecting devices more than once; reflecting, usingthe single element, a first part of the first portion of the beam;generating another portion of the output beam by exiting the first partof the first portion of the beam from the system; and transmitting,using the single element, a second part of the first portion of the beamto repeat the cycle, wherein the cycle ends after traversal between thefirst and second reflecting devices, such that the first part of thefirst portion of the beam is reflected, the first part of the firstportion exits the system, and the second part of the first portion ofthe beam is transmitted.
 14. The method of modifying a beam of claim 13,wherein beginning a cycle during which the beam travels through thesystem further comprises: enabling a beam path from the first curvedreflecting device to the second curved reflecting device to create afirst segment of the cycle; enabling a beam path from the second curvedreflecting device to the first curved reflecting device to create asecond segment of the cycle; enabling a beam path from the first curvedreflecting device to the second curved reflecting device to create athird segment of the cycle; and enabling a beam path from the secondcurved reflecting device to the single element to create a fourthsegment of the cycle.
 15. The method of modifying a beam of claim 13,wherein providing first and second curved reflecting devices furthercomprises: providing a first confocal mirror for the first curvedreflecting device; and providing a second confocal mirror for the secondcurved reflecting device.
 16. The method of modifying a beam of claim13, further comprising: increasing pulse size of the first portion ofthe beam by using the parallel plate optical element while maintaining aconstant divergence to increase Etendue of the output beam.